It has been conventionally proposed that a heat-generating body utilizing a heat-generating composition containing metallic powder, such as iron powder, as a major component in a powder form, a paste form or the like and utilizing reaction heat with oxygen in air is applied to a footwear, such as shoes, slippers, to warm foot.
For example, it has been proposed that a housing part of the heat-generating body is formed in a sole insert of a shoe, and a heat-generating body charged in an air permeable bag is provided inside the housing part (JP-A-U-S61-8013).
Such a heat-generating body for keeping heat in a shoe has also been proposed that has a heat-generating body in a shoe sole form having black kraft paper attached on an inside thereof (JP-A-U-H3-7706).
Furthermore, such a heat-generating body for foot such as for a shoe has been proposed in that a heat-generating agent is charged in a flat air permeable bag body having a shape adapted for a partial shape of foot, and a non-transferable adhesive agent layer is provided on one surface of the air permeable bag body, whereby it is adhered to the surface of foot with the non-transferable cohesive agent layer (JP-A-H2-172460).
A method for fixing a heat-generating composition with a cohesive agent is proposed in JP-A-S62-347, but it is substantially impossible to adhere a powder heat-generating composition on an inside of a bag body in practical productions, and even if it is possible, it lacks in practicability because the adhesion strength is small to fail to attain complete fixing, which causes releasing during the use, the use feeling is deteriorated due to a platy shape having poor flexibility, and in addition, contact with air is considerably impaired due to the presence of the mixed adhesives to cause nonuniformity and fluctuation in temperature.
Other proposals of heat-generating bodies for warming foot have been made, for example, in JP-A-H2-154762, JP-A-H5-115310, JP-A-U-H6-21616, JP-A-U-H5-84317 and JP-A-H5-176951.
Such a process has been generally employed as a process for producing the heat-generating body for warming foot in that after dropping a powder heat-generating composition containing water on a prescribed region of a base material, a covering material having air permeability is overlaid thereon, and thereafter, a peripheral part of the base material and the covering material is sealed wholly by heat sealing, a hot-melt adhesive or the like.
In alternative, such a process is employed in that a heat-generating composition in a viscous cream form is laminated on a base material in a film or sheet form by printing, which is covered with a covering material, and a peripheral part of the base material and the covering material is sealed wholly by heat sealing, a hot-melt adhesive or the like.
Examples of the conventional heat-generating body for warming foot include the one formed by mixing, in addition to metallic powder, such as iron powder, and water, activated carbon for accelerating heat generation, a metallic chloride for continuously inducing a heat-generating reaction by breaking an oxide film on the surface of the metallic powder, a water absorbing agent for preventing tackiness, and the like in conventionally suitable proportions, and the heat-generating composition is in a powder form containing water and is dropped on a base material.
Examples of the method for dropping the powder heat-generating composition include a method of moving the base material intermittently and dropping the heat-generating composition during suspension of the base material, and a method of moving the base material at a constant velocity, and dropping the heat-generating composition on the base material while moving the dropping mesh for dropping the heat-generating composition at the same velocity as the base material.
Furthermore, a production using a lamination method and the like by printing, such as screen printing, coating and the like is also employed for a paste heat-generating composition formed into a viscous heat-generating composition by adding viscosity to the heat-generating composition by containing a thickener (JP-A-H9-276317).
A heat-generating body for warming foot having a prolonged heating duration is difficult to produce at a high speed, and migration of the heat-generating composition inside the container bag occurs upon use to deform the heat-generating body itself, and thus the use feeling is considerably deteriorated. On the other hand, such a heat-generating body for warming foot that can be produced at a high speed, in which the heat-generating composition does not move inside the container bag during use to prevent the heat-generating body itself from deformation has a short heating duration and has problems as a practical product.
There has been no heat-generating body for warming foot with good use feeling that can be produced at a high speed, has a prolonged heating duration, is free of migration of the heat-generating composition inside the container bag upon use to prevent the heat-generating composition itself from deformation.
That is, in a heat-generating body for warming foot having a conventional powder heat-generating composition, the heat-generating body for warming foot is bulky in total and is poor in texture with stiff feeling. Furthermore, it is poor in flexibility and is difficult to fit complex unevenness and curved surfaces with small curvature on the surface of a human body. Moreover, since the elongation property or the stretch property is lowered, the heat-generating composition moves associated with movement of the human body, and the heat-generating body is deformed, whereby the followability of the heat-generating body to the surface is deteriorated to cause such a problem that the use feeling is considerably deteriorated.
The heat-generating body having a conventional powder heat-generating composition can follow only a rough curved surface and partially causes warpage due to misfit in curved surfaces depending on the kind of shoes, so as to cause pain on foot by pressing foot, whereby the applicable shoes are restricted to provide significant unsatisfaction.
In the heat-generating body having a conventional powder heat-generating composition, although the heat-generating composition is imparted with wettability with water, the mixing ratio of water is as low as such an extent that is suitable for the heat-generating reaction, and it is in the form of powder and is poor in flowability. Therefore, it is considerably difficult to be uniformly distributed within the prescribed region on the base material, and thus the thickness of the heat-generating composition is fluctuated inside the heat-generating body for warming foot, whereby the heat-generating composition moves inside the inner bag, or the heat-generating composition is deviated due to deviation and bending thereof, so that the thickness of the heat-generating composition inside the heat-generating body for warming foot becomes unequable. Accordingly, in the case where it is used by fixing on a human body, it causes such serious problems in that there are cases where ambustion occurs due to the unevenness in heat generation temperature distribution upon using by fixing on the same position, the skin receives a powerful stimulus, dermopathy, such as rubefaction, eruption, skin fit, arises.
In the method for fixing a powder heat-generating composition with an cohesive, it is substantially impossible upon practical production that the powder heat-generating composition is adhered on the inside surface of the bag material, and even when it is possible, the adhesion strength is small to fail to attain complete fixation, but it is released during use, and only a plate-like material with poor flexibility is obtained to impair practicality by deteriorating use feeling and by causing unevenness and fluctuation in temperature.
On the other hand, a heat-generating composition using a thickener having a viscous paste or cream form is good in moldability to retain uniformity in thickness, but is restricted in practicality because drainage of excessive water is insufficient, and desired heat generation amount and heat generation duration cannot be obtained due to influences of the thickener and a binder to fail to produce a large size product and to fail to obtain a prolonged heat-generating duration.
In the case of the viscous heat-generating composition in a paste or cream form, if the adhesiveness to a base material is poor, a laminated material is peeled from the base material upon molding by pulling by an unlaminated heat-generating composition due to cohesiveness of the heat-generating composition, so as to cause unevenness in thickness, and there are some cases where a normal sole shape cannot be obtained to restrict the base material.
In the conventional powder heat-generating composition or the conventional semi-kneaded heat-generating composition, because water is mixed only in such an amount that is suitable for the heat-generating reaction, the heat-generating reaction smoothly and continuously proceeds immediately upon contacting with air. As a result, the heat-generating reaction occurs after mixing the heat-generating composition but before charging the heat-generating body thus produced in an outer bag, and the vapor pressure of water in the heat-generating composition is increased to expand the heat-generating body, so as to cause such a problem in that the expanded heat-generating body is difficult to be charged in a packing bag having air nonpermeability.
Furthermore, in the conventional heat-generating composition, a heat-generating reaction occurs after mixing the heat-generating composition but before charging the heat-generating body thus produced in an outer bag to cause loss due to the heat-generating reaction and to deteriorate the quality of the heat-generating composition, and furthermore, the reaction product formed by the heat-generating reaction is solidified causes various problems, such as reduction in yield, difficulty in handling, complication in maintenance of a production apparatus, restrictions in operation time of a production apparatus and in working time of an operator, difficulty in processing the solidified matter, and the like problems.
In the method of intermittently moving a base material and dropping a heat-generating composition during suspension of the base material, there is a problem that the production rate is lowered due to the frequent repetition of suspension and start-up of the base material.
In the method of moving a base material at a constant velocity and dropping the heat-generating composition on the base material while moving the dropping mesh for dropping the heat-generating composition at the same velocity as the base material, although the production rate can be increased since substantially no repetition of suspension and start-up of the base material occurs, a complicated mechanism is necessary for moving the dropping mesh for dropping the heat-generating composition at the same velocity as the base material, and moreover, there is a problem that the velocity of moving the mechanism is greatly restricted because the heat-generating composition contains powder and water and is poor in flowability.
Although the conventional powder heat-generating composition is imparted with wettability with water, the mixing ratio of water is as low as such an extent that is suitable for the heat-generating reaction, and it is extremely poor in flowability, whereby it is significantly difficult that the composition is uniformly distributed within the prescribed region on the base material only by simply dropping thereon.
Therefore, the distribution of the heat-generating composition is uniformized to a certain extent with a roller upon sealing with a covering material overlaid, but there is such a tendency that the distribution of the heat-generating composition is deviated to the origination side of conveying the bag material owing to the nature of the powder heat-generating composition.
The semi-kneaded heat-generating composition is such a heat-generating composition that is formed by mixing all the components including a binder at suitable proportions, and it is necessarily subjected to a tableting step, so as to complicate the process.
A heat-generating composition in a slurry form with less viscosity cannot maintain the shape to fail to attain molding into a constant shape, and it is then molded through a complicated step, such as paper making.
There are demanded a heat-generating composition having moldability, shape maintenance property, and heat generation characteristics enabling a prolonged heat generation time at the same time, a heat-generating body using the same, and a simple production process therefor.